1. Field of the Invention
The present invention relates to a printing device for an office machine, e.g. a typewriter, accounting machine or teleprinter, of the type in which a driving means normally causes a type head to rotate and in which a change-over mechanism arrests the head, thus selecting the character to be printed, and transfers the motion of the driving means to a striking mechanism to effect the printing of the selected character, such a device being referred to herein as of the type defined.
2. Description of the Prior Art
A device of the type defined is known wherein the motion of the driving means is transferred to the head and to a striking cam by a differential which normally causes the head to rotate, the striking cam being held stationary. By means of the simultaneous energization of two electromagnets, a selector disc connected to the head is arrested to arrest the head in the angular position corresponding to the character to be printed and the striking cam is released for command of the striking of the selected character or type. This device, however, has the disadvantage of using two different means for the selection and striking operations. Moreover, while the electromagnet which commands the striking can be deenergized immediately once the striking cam with which it co-operates has been released, assuming this electromagnet to trigger a one-cycle clutch, the electromagnet which co-operates with the selector disc must remain energized until such time as the striking cycle has been completed. This requires a heavily rated and costly selector electromagnet and a fairly complex circuit capable of generating the actuating command for this electromagnet.